The present application claims priority to Japanese Application No. P2000-218646 filed Jul. 19, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a method of production of a multilayer optical recording medium obtained by stacking a plurality of optical recording layers for optically recording information.
2. Description of the Related Art
Recently, in the field of information recording, studies on the method of optical information recording are underway everywhere. Optical information recording systems have numerous advantages such as the fact that non-contact recording and reading are possible, and it is possible to handle various forms of memories such as the reading-only type, write-once type, and rewritable type, etc. This system has broad potential applications from industrial to consumer use as a system able to realize inexpensive and large size files.
Among these, in particular, optical disks designed for use as reading-only type memories, that is, high density information recording media and optical video disks called xe2x80x9cdigital audio disksxe2x80x9d,xe2x80x9cdigital versatile disksxe2x80x9d, etc. have come into wide use.
This type of optical disk is configured by a transparent substrate formed with a pattern of irregularities such as pits to represent signal information and grooves, that is, an optical disk substrate, a reflection film comprised of an aluminum film or other metal thin film formed on the substrate, and a protection film for protecting the reflection film from moisture and oxygen in the air formed on the reflection film. When reading information of such an optical disk, for example, laser or other light for reading is focused on the pattern of irregularities from the optical disk substrate side and information is detected from the difference of reflectivity between the incident light and the returning light.
When producing such an optical disk, first, an optical disk substrate having the above pattern of irregularities is formed by a method such as injection molding, a reflection film comprised of a metal thin film is formed by vapor deposition or other method on this, and an ultraviolet light setting resin etc. is coated on this to form a protection film.
Recently, the demand for larger capacities of such optical disks has increased. To meet with this, an optical disk has been proposed which is obtained by forming a pattern of irregularities on one surface of the optical disk substrate, forming a semi-transparent film over this, forming a pattern of irregularities on this semi-transparent film separated by a distance of several 10s of xcexcm, and forming a reflection film over this to thereby give a total of two optical recording layers.
The above optical disk having a plurality of optical recording layers has a large capacity and is expected to improve productivity and to be able to be produced easily.
As the method for the above, for example, there is the method of coating an ultraviolet light setting resin on a stamper having a pattern of irregularities, curing this by irradiating ultraviolet light while pressing a flexible film, then separating the stamper to transfer the pattern of irregularities to the ultraviolet light setting resin cured in a state bonded to the flexible film, forming a semi-transparent film on the pattern of irregularities of the obtained cured resin film to form the first stack having one optical recording layer, on the other hand, forming a substrate having a pattern of irregularities by injection molding, forming a reflection film on the obtained pattern of irregularities to similarly form the second stack having one optical recording layer, then bonding together the first stack and the second stack.
However, in the above conventional method of production of an optical disk having a plurality of optical recording layers, it is difficult to separate the stamper from the resin cured by irradiating the ultraviolet light, so there arise problems that burrs may occur on the cured resin or the resin may adhere on the stamper causing a reduced lifetime of the stamper.
In addition, in the step of forming a semi-transparent film on the cured resin film adhered on the flexible film, since a flexible film is used, it is not easy to handle. Therefore, there also arise problems that film formation is difficult and the flexible film becomes wrinkled during the film formation.
The present invention was made in consideration of this situation and has its object to provide a method of production of a multilayer optical recording medium able to be produced without the accompanying difficulty in separating a stamper and while avoiding the difficulties in forming a semi-transparent film etc. on a thin flexible film.
According to a first aspect of the present invention, there is provided a method of production of a multilayer optical recording medium comprises the steps of forming a first optical recording layer on a substrate formed with a pattern of irregularities, forming a transfer substrate comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof, forming a second optical recording layer on the pattern of irregularities of the transfer substrate, adhering a flexible film at the upper portion of the second optical recording layer by an adhesive layer, separating the second optical recording layer and the transfer substrate at their boundary to transfer the second optical recording layer to the flexible film, and bonding together the first optical recording layer and the second optical recording layer with them facing each other.
In the method of production of a multilayer optical recording medium of the present invention, preferably the first optical recording layer is formed by a reflection film.
In the method of production of a multilayer optical recording medium of the present invention, preferably the second optical recording layer is formed by a semi-transparent film.
In the method of production of a multilayer optical recording medium of the present invention, preferably the second optical recording layer is formed by sputtering.
In the method of production of a multilayer optical recording medium of the present invention, preferably the second optical recording layer is made from a material including at least one of aluminum, silver, and silicon.
In the method of production of a multilayer optical recording medium of the present invention, a first optical recording layer is formed by a reflection film etc. on a substrate formed with a pattern of irregularities. On the other hand, a transfer substrate is formed which is comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof. Next, a second optical recording layer is formed by a semi-transparent film, etc. on the pattern of irregularities of the transfer substrate. Next, a flexible film is adhered at the upper portion of the second optical recording layer by an adhesive layer. Next, the second optical recording layer and the transfer substrate are separated at their boundary to transfer the second optical recording layer to the flexible film. Next, the first optical recording layer and the second optical recording layer are bonded together with them facing each other.
Therefore, production is possible without requiring the step of separating a stamper from a resin cured by irradiating ultraviolet light and the step of forming a semi-transparent film on a thin flexible film. Production is possible without the accompanying difficulty in separating the stamper and while avoiding the difficulties in forming a semi-transparent film on a thin flexible film.
According to a second aspect of the present invention, there is provided a method of production of a multilayer optical recording medium comprises the steps of forming a first optical recording layer on a substrate formed with a pattern of irregularities, forming a first transfer substrate comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof, forming a second optical recording layer on the pattern of irregularities of the first transfer substrate, adhering a flexible film at the upper portion of the second optical recording layer by an adhesive layer, separating the second optical recording layer and the first transfer substrate at their boundary to transfer the second optical recording layer to the flexible film, forming a second transfer substrate comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof, forming a third optical recording layer on the pattern of irregularities of the second transfer substrate, bonding together the third optical recording layer and the first optical recording layer with them facing each other, separating the third optical recording layer and the second transfer substrate at their boundary to transfer the third optical recording layer onto the first optical recording layer, bonding together the second optical recording layer and the third optical recording layer with them facing each other.
In the method of production of a multilayer optical recording medium of the present invention, preferably the third optical recording layer is formed by a semi-transparent film.
In the method of production of a multilayer optical recording medium of the present invention, preferably after the step of transferring the third optical recording layer onto the first optical recording layer, steps of forming a transfer substrate comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof, forming an optical recording layer on the pattern of irregularities of the transfer substrate, and adhering the optical recording layer by an adhesive layer to transfer the optical recording layer are repeated.
According to a third aspect of the present invention, there is provided a method of production of a multilayer optical recording medium comprises the steps of forming a first optical recording layer on a substrate formed with a pattern of irregularities, forming a first transfer substrate comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof, forming a second optical recording layer on the pattern of irregularities of the first transfer substrate, adhering a flexible film at the upper portion of the second optical recording layer by an adhesive layer, separating the second optical recording layer and the first transfer substrate at their boundary to transfer the second optical recording layer to the flexible film, forming a second transfer substrate comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof, forming a third optical recording layer on the pattern of irregularities of the second transfer substrate, bonding together the third optical recording layer and the second optical recording layer with them facing each other, separating the third optical recording layer and the second transfer substrate at their boundary to transfer the third optical recording layer onto the second optical recording layer, bonding together the first optical recording layer and the third optical recording layer with them facing each other.
In the method of production of a multilayer optical recording medium of the present invention, preferably the third optical recording layer is formed by a semi-transparent film.
In the method of production of a multilayer optical recording medium of the present invention, preferably after the step of transferring the third optical recording layer onto the first optical recording layer, steps of forming a transfer substrate comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof, forming an optical recording layer on the pattern of irregularities of the transfer substrate, and adhering the optical recording layer by an adhesive layer to transfer the optical recording layer are repeated.
In the method of production of a multilayer optical recording medium of the present invention, a first optical recording layer is formed by a reflection film etc. on a substrate formed with a pattern of irregularities.
On the other hand, a first transfer substrate is formed which is comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof. Next, a second optical recording layer is formed by a semi-transparent film, etc. on the pattern of irregularities of the first transfer substrate. Next, a flexible film is adhered at the upper portion of the second optical recording layer by an adhesive layer. Next, the second optical recording layer and the first transfer substrate are separated at their boundary to transfer the second optical recording layer to the flexible film.
Next, a second transfer substrate is formed which is comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof. Next, a third optical recording layer is formed by a semi-transparent film etc. on the pattern of irregularities of the second transfer substrate. Next, the third optical recording layer is transferred onto the first or second optical recording layer.
Next, the third optical recording layer is bonded to the first or second optical recording layer together with them facing each other.
Therefore, when an optical disk having three optical recording layers is produced, therefore, production is possible without requiring the step of separating a stamper from a resin cured by irradiating ultraviolet light and the step of forming a semi-transparent film on a thin flexible film. Production is possible without the accompanying difficulty in separating the stamper and while avoiding the difficulties in forming a semi-transparent film on a thin flexible film.
Further, it is possible to produce an optical disk having four or more optical recording layers by repeating steps of forming a transfer substrate comprised of an acrylic resin formed with a pattern of irregularities on a surface thereof, forming an optical recording layer on the pattern of irregularities of the transfer substrate, and adhering the optical recording layer by an adhesive layer to transfer the optical recording layer after the step of transferring the third optical recording layer onto the first optical recording layer.